Why do turntable belts disolve?

[hayerjoe]

hello everyone

I've been working for the first time on belt driven record players. Each one has had a totally dissolved turntable belt. In some ways this is good because the decks are abandoned as they don't work so I pick them up for next to nothing, but on the other hand some of them are a right pain to fix.

BUT I'm intriqued as to why rubber belts from the 80s disolve into virtually a liquid but rubber idler wheels from 20 years further back do not turn liquid. Did they use some new fangled rubber in the 80s that proved longterm to be a bad idea? or did an idler use a different rubber as it was more used in compression rather than belts that needed to be elastic?

Any chemists out there who can explain the melting belt, hardening idler phenomenon?

Cheers
Joe

[Tractorfan]

Hi,
That's puzzled me too. It seems that a lot of early rubbers, foams and plastics were chemically unstable back then,
Early Philips audio tape and video recorders were famous for it, also, those new fangled loudspeaker suspension surrounds often crumbled to dust after 30 odd years.
As a lad, I had a model of a hay bale conveyor made by 'Britain's' models. It was made from two different types of plastic, a rigid one for the frame and a flexible one for the conveyor belt, which reacted with each other and effectively destroyed it.
Cheers, Pete.

[Nuvistor]

Some reading.
https://www.polymerdatabase.com/poly...lastomers.html

[hayerjoe]

Originally Posted by Nuvistor

Some reading.
https://www.polymerdatabase.com/poly...lastomers.html

Interesting, so as both belts and idler wheels are in the same heat and ozone environment (ie under a platter) they simply must have been a different 'type' of rubber as per that link

Do modern turntable belts suffer the same problems? I mean has the issue been addressed or is it something unavoidable if you want a stretchy belt?

[hayerjoe]

plus, thinking about it there is something unusual about turntable belts. in the same "music centres" that have totally liquid turntable belts, I've NEVER come across a cassette belt that had melted, and they'd be made of the same stretch type rubber, of the exact same vintage.

[Refugee]

There are two types of rubber used.
One type smells when new and goes brittle after some years.
The other type smells less when new and goes sticky as the oil it is made from does not evaporate.

[Nuvistor]

Originally Posted by hayerjoe

plus, thinking about it there is something unusual about turntable belts. in the same "music centres" that have totally liquid turntable belts, I've NEVER come across a cassette belt that had melted, and they'd be made of the same stretch type rubber, of the exact same vintage.

Some one will know but didn’t the Philips cassette belts turn to goo?

[paulsherwin]

It all depends on the composition of the belts. Some of the belts made in the 1970s have a particular propensity to turn to goo, while others just lose their stretchyness.

Cassette deck belts certainly deteriorate though may not go gooey. Pretty much all decks made before 1990 will have needed their main capstan belts changing by now, and 1990s models will be on borrowed time.

[deswradio]

Really interesting observations in this thread - and cassette decks are definitely not all immune. I tackled a Pioneer music centre a few weeks ago where the belts had disintegrated into many pieces and those pieces had fallen into (and jammed) other parts of the mechanism. A good day for organic solvents.

As far as I can judge, there are three main type of "rubber", one, natural rubber which is a gooey sticky thing and is made useful by vulcanising with sulphur which cross bonds the rubber molecules, used it tyres to this day. Two, plasticised plastics where a low evaporation solvent makes a rigid plastic rubbery. And three intrinsically rubbery stuff like polyurethane which lasts for ages.

[paulsherwin]

All the recent belts I've seen seem to be made with some sort of neoprene. Maybe they will have longer lives.

[Nickthedentist]

I've certainly had an early 1980s Marantz cassette deck liquify, and an mid-1990s Sony one too.

[Lloyd 1985]

I’ve got a Sharp VZ-3500, the vertical turntable with radio and cassette deck, that had suffered from rubber turning to goo, the main turntable belt had gone really badly, spread itself everywhere! And the pinch roller had also turned into a gooey blob, luckily I spotted it before trying a tape in it! Strangely all the cassette belts are fine.

Another much newer item is a Panasonic mini Hi-Fi system from around 2004, the pinch rollers in that have gone rock hard, and they are the smaller diameter ones as it’s got auto reverse. It still plays, but it doesn’t do the tapes any good at all! I was quite surprised by this one, as it’s not that old.

Regards
Lloyd

[emeritus]

I first noticed this with the tyre fitted to the motor that powered my Philips EL3585 tape recorder. I used to have to replace the motor every few years (worn-out brushes that gouged grooves n the commutator due to the very heavy use I made of it) but kept the old ones in my box of odds and ends. In the mid-1970's the tyre on a motor dating from circa 1967 had liquified. The same sort of problem affects the grippy coating used for some expensive binoculars and cameras. Seemingly the type of plastic that has excellent grippyness when new, is prone to deteriorate after a few years.

[nickdoofah]

I have repaired DOZENS possibly even more Boomboxes/Hifi cassette decks where the belts have turned to goo! A Sharp GF-250 boombox also had a pinch roller turned to goo!I saw the same in a GF-7500 too (Same deck)

[TIMTAPE]

It's not always appreciated that even the best rubber parts deteriorate with time, regardless of whether the gear is used or not. If we rarely if ever actually use a turntable or a tape machine to play a record or tape and dont keep a note of when we last replaced the belts, it may only seem as if the belts have prematurely failed.

[Diabolical Artificer]

If you consider the short amount of time synthetic rubbers had been around it's no wonder it degraded.That and the very short time a lot of the commercial products like tape recorders had been around. In the case of tape cassette based recorders about 20 years.

It's interesting to note that early reel to reel tape decks only used one rubber belt, that for the tape counter. A lot of the break through's on synthetic rubber & plastic chemistry happened 1953 with 6 Nobel prizes issued that year,see - https://en.wikipedia.org/wiki/Polymer

From what I've been able to find there are two main types of degradation of rubber, cracking - ozone cracking - https://en.wikipedia.org/wiki/Ozone_cracking and other degardation caused by environmental conditions like heat and stress and reversion - https://www.polymersolutions.com/blo...ber-reversion/.

Andy.

[Nuvistor]

Originally Posted by Diabolical Artificer

If yIn the case of tape cassette based recorders about 20 years.

Andy.

Perhaps a little longer, Philips prototype introduced at the Berlin show in 1963.
Admittedly small portable machines but full recording/playback.
https://en.wikipedia.org/wiki/Cassette_tape

[theredhouseinn]

Back in the 50's the Grundig TK series r to r decks used a round belt to drive the capstan flywheel. This belt used to stretch and go misshapen. We found that if you put the belt in very hot water for about 15 seconds the belt shrunk back to its original size and perfect circle. Never had one of these belts disolve into black goo like the later r to r's and cassette decks.
John.

[majex45]

I have two cassette decks (a Seoum & NAD) where the belts have turned to goo. However the belt in the Seoum that drives the counter is still OK.
The mirror surround on my Canon A1 camera went the same way.
I also had a slide digitiser that was covered in "touchy-feely" material and the stuff tourned to goo, I had to throw it away as it was getting all over the contents of the cupboard it was stored in - and it's very sticky, black and hard to get rid of. Yuk!